The present invention is directed to a method and to an apparatus for co-planarity testing and/or for slanted attitude testing of a contact row of SMD components.
In the automatic onserting (equipping or mounting) of printed circuit boards or ceramic substrates with SMD components (SMD=surface mounted device), the individual components are taken from a magazine or a delivery means, e.g., a bulb with an onserting head and are then positioned on the printed circuit board or the ceramic substrate in a predetermined position. Since the components in the magazine or in the fetching position of the delivery means exhibit a positional tolerance of 1 mm, but must be positioned with high precision on the printed circuit board or on the ceramic substrate, an automatic position recognition and correction is required. Further, particularly given SMD components having a great number of terminals, the co-planarity, i.e. the uniform height position of the terminals, must be checked. Such a check is also to be implemented, for example, as a quality control check during the manufacture of SMD components.
WO 93/19577 discloses a shadow-casting method for co-planarity measurement of components. The terminals are individually illuminated by transmitted light and the shadowgram of the terminal end of an SMD component is projected onto a sensor. The optical axis of the imaging has a defined angle unequal to 90.degree. relative to the horizontally arranged object. The height position of the terminal can be calculated from the angle, the spacing of the terminal from the sensor and the position of the shadowgram on the sensor. As a result of different component sizes and different component positions present in the arrangement, blurred imagings of the shadow of the terminals on the sensor arise in this method. Moreover, the position of the shadow on the sensor can shift when the component is farther from the sensor, so that the evaluation of the height position is more difficult. In addition, this method is very time-consuming, particularly given components with a great number of terminals, since every individual terminal must be investigated.